1. Field of the Invention
This invention relates to a dry-type microscope objective lens. Especially, this invention relates to a dry-type microscope objective lens which has a high NA (numerical aperture) in the range from low magnification to middle magnification and is lightweight.
2. Description of the Related Art
A microscope is required to satisfy both capabilities for high speed scanning and for high resolution at the same time, for example, in the case of making a virtual slide. An optical system having a wide field of view on the object side is desired in order to achieve high speed scanning, and an optical system having a large object-side numerical aperture (NA) is desired in order to achieve high resolution.
Accordingly, a large number of objective lenses which are a lens of about 20 magnifications and have a high NA (numerical aperture) are used for observation with a microscope at present. For example, U.S. Pat. No. 6,501,603 B1, Japanese Patent Kokai No. 2005-189732, Japanese Patent Kokai No. 2007-133071, U.S. Pat. No. 7,382,542 B1, Japanese Patent Kokai No. Hei 11-249024, U.S. Pat. No. 5,920,432, and US 2008/0180805 disclose microscope objective lenses of about 20 magnifications which have a high NA.
U.S. Pat. No. 6,501,603 B1 discloses a dry objective lens of 20 magnifications which has an object-side NA of 0.8 and a water immersion objective lens of 20 magnifications which has an object-side NA of 0.9 to 0.95.
Japanese Patent Kokai No. 2005-189732 discloses a water immersion objective lens of 16 magnifications which has an object-side NA of 0.8.
Japanese Patent Kokai No. 2007-133071 discloses an oil immersion objective lens of 20 magnifications which has an object-side NA of 0.95.
U.S. Pat. No. 7,382,542 B1 discloses a water immersion objective lens of 20 magnifications which has an object-side NA of 1.0.
Japanese Patent Kokai No. Hei 11-249024 discloses a water immersion objective lens of 20 magnifications which has an object-side NA of 0.75.
U.S. Pat. No. 5,920,432 discloses a dry objective lens of 10 magnifications which has an object-side NA of 0.5 and a dry objective lens of 20 magnifications which has an object-side NA of 0.75.
US 2008/0180805 discloses a dry objective lens of 10 magnifications which has an object-side NA of 0.8.